Stop reporting refused external avatars to Sentry

app/commands/user/avatar_data_uri.rb

@@ -35,6 +35,13 @@ def call
     return nil if external_avatar_url.blank?
 
     external_data_uri
+  rescue OpenURI::HTTPError => e
+    # A 4xx means the host has refused or lost this user's avatar (a deleted
+    # account, or a host that blocks us). That is a fact about the user's data,
+    # so we fall back without reporting it. A 5xx may be transient, so it still
+    # goes to Sentry.
+    Sentry.capture_exception(e) unless e.io.status.first.start_with?("4")
+    nil
   rescue StandardError => e
     Sentry.capture_exception(e)
     nil

test/commands/user/avatar_data_uri_test.rb

@@ -70,6 +70,15 @@ def png_bytes = File.binread(Rails.root.join("app", "images", "favicon.png"))
     assert_nil User::AvatarDataUri.(user)
   end
 
+  test "returns nil without reporting when the external avatar host refuses the request" do
+    user = create :user, :external_avatar_url
+    stub_request(:get, user.attributes['avatar_url']).to_return(status: 403)
+
+    Sentry.expects(:capture_exception).never
+
+    assert_nil User::AvatarDataUri.(user)
+  end
+
   test "returns nil rather than raising when the external avatar is not an image" do
     user = create :user, :external_avatar_url
     stub_request(:get, user.attributes['avatar_url']).to_return(